Mexico) Petroleum Potential
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UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Brief on Reforma-Campeche's (Mexico) Petroleum Potential by Bernardo F. Grossling U.S. Geological Survey Open-file Report 79-237 This report has not been edited or reviewed for conformity with U.S. Geological Survey standards or nomenclature BRIEF ON REFORMA-CAMPECHE'S (MEXICO) PETROLEUM POTENTIAL Opportunities and Challenges for the United States For the past several months I have been endeavouring to gauge the petroleum prospects of southeastern Mexico on the basts of the published technical literature, newsmedia accounts, and critical examination of the data from a geologic point of view. The main results of this study are briefly summarized here, and will be reported in greater detail at a later date. 1) In May 1972 Petroleos Mexicanos (Pemex), the national oil company of Mexico, discovered a very important new petroleum province through two wildcat wells completed a day apart. These wells are about 50 km south west of the City of Villahermosa, State of Chiapas. The well Sitio Grande-1, completed May 8, 1972, found at 4,120 m depth a Middle Cretaceous dolomitic pay zone, over 200 m thick. The well Cactus-1, completed May 9, 1972, found at 3,360 m depth an Upper Cretaceous to Lower Cretaceous calcarenite to dolomitic limestone pay, about 200 m thick. Cactus-1 tested initially 1,694 barrels of oil per day and 5.7 million cubic feet of gas per day through a 8 mm choke. These were the first finds of Cretaceous oil in southeastern Mexico. 2) From the information now on the public record, it is apparent that the magnitude of the petroleum resources of the new province may be second, in the sense of a single province, only to those in the Middle East province. The aggregate petroleum potential of the U.S.S.R. is of course substantial, but it is distributed in several petroleum provinces. For briefness, I will refer to the new Mexican find as the Reforma-Campeche Province. Moreover, the geologic conditions in other parts of Mexico's Gulf Coast are such that one can reasonably suspect that the ultimate potential of the country may turn out to be much larger than what can be projected now from the Reforma-Campeche Province as the main base of projection. 3) Until 1938 Mexico's petroleum industry was in private hands, consisting mainly of international corporations. In 1938 the government of President Lazaro Cardenas expropriated the industry, establishing Pemex to carry out the country's petroleum development. A downward drift of Mexico's petroleum sector which occurred during the initial years of Pemex was arrested when in 1949 President Aleman appointed Senator Antonio Bermudez to head Pemex. Bermudez gave a very dynamic stance to Pemex that provided the base for its later successes. 4) The petroleum prospective sedimentary areas of Mexico consist of about 690,000 sq. km. onshore and about 440,000 sq. km. in the continental shelves down to the 200 m water depth line, (Grossling, 1976). The bulk of these prospective areas extend along the Gulf Coast plain, from Chihuahua and Coahuila in the northeast to the Yucatan Peninsula in the southeast. There is also a significant prospective area in the western part of Baja California. Also the continental slope, that is beyond the edge of the continental shelf, along Mexico's Gulf Coast appears to be of petroleum interest. 5) Mexico's oil production began in 1901 in the State of Tabasco, which is one of the States where about 70 years later the Reforma- Campeche discovery was to be made, Fig. 1. Mexico's annual production peaked at 193 million barrels in 1921, and then dropped in 1932 to a low of 33 million barrels. Production slowly recuperated, reaching in 1973 a level of 191 million barrels. Since 1973 Mexico's oil production has been rapidly expanding. The 1977 production of crude oil, condensate and absorption liquids was 396 million barrels, of which 75 million barrels were exported. For 1982 a production of 2.7 million barrels per day (equivalent to about 985 million barrels for the year) is being forecasted by Pemex, of which over one million barrels per day would be exported. 6) The productive trend which may be called the Reforma-Campeche trend appears to be controlled by a broad antic!inorium, about 120 km wide in the Reforma onshore area. In the neighborhood of Reforma it trends NW-SE. The trend extends northeastward, under a cover of Tertiary and Quarternary sediments, along the Campeche shelf. The distance from the southernmost wells drilled to the Ixchel well, the northernmost drilling undertaken so far, is about 500 km. Pemex has not disclosed officially yet the results of Ixchel production tests, but considers it to be an important discovery within a highly prospective area (Petroconsultants, S.A., report). The Macuspana Tertiary Basin lies roughly to the east of the antic!inorium and the Saline and Veracruz Basins to the west and northwest. 7) The productive trend is determined stratigraphically by a trend of Lower to Middle Cretaceous reefs, which in the Reforma area itself run NW-SE, and then curve northeastward following more or less the western edge of the Campeche Bank. The reef trend appears to extend eastward of the Cordoba Platform to just south of the Reforma area where it turns to the northwest. The above-mentioned antic!inorium, of the Reforma area, extends to the north under a cover of later sediments. 8) The initial Reforma discovery was in Upper to Lower Cretaceous rocks, but subsequently production has been found also in Eocene, Paleocene, and Jurassic formations. The Cretaceous carbonates are separated by a major unconformity from the overlying Tertiary elastics. The Tertiary formations provide the seal, and the source rocks are believed to be marine Jurassic shales. 9) The productive structures are anticlinal domes cut by normal and transverse,, faults, which subdivide each main structure in a number of blocks. Some of the onshore and offshore seismic structures are outlined in Fig. 2. The movement of the underlying Jurassic salt during the Laramide orogeny significantly affected the pattern of structural deformation of the Cretaceous carbonate section, and has contributed to the structural complexity. The drilling depths to the pay tops in the onshore Reforma area have so far ranged from 3,646 m to 4,613 m, but the producing formations are shallower and in younger stratigraphic positions in the offshore continua tion of the productive trend on the Campeche Bank. For instance, in the group of structures Abcatun, Akal, Bacab and Chac the depth to pay top has ranged from 1,300 to 3,545 m. Pemex expects that the Cretaceous rocks which are productive in the onshore Reforma area may be productive offshore, but apparently this has not been established yet. 10) The exceptional character of the Reforma-Campeche province is revealed by many factors thicknesses of the oil columns, pay porosities and permeabilities, well productivities, success ratio of the exploratory drilling, area! _extent_of the individual fields and the apparent length of the productive trend as a whole. According to Pemex (March, 1978), the fields presently under production in the onshore Reforma area range from 45 to 150 km2 in areal extent, and have oil columns ranging from 300 to 1,000 m. In some blocks of the Bermudez field the oil column has been stated to be more than 2,000 m thick; early in 1977 it was discovered that Samaria, Iride, and two smaller fields were in fact a single accumulation with four structural highs, which was then named Bermudez. If the report of the 2,000 m plus oil column is correct, it may establish one of the thickest if not the thickest oil column found yet in the earth. Pemex has indicated that in the onshore area the oil columns in the various fields are generally over 500 m thick. The pay porosities and permeabilities are stated to be very large. This is clearly due to the detrital character of the rocks, tectonic frac turing, subaqueous solution, and dolomitization. The average well productivity, in the producing fields, is about 5,500 barrels per day. The success ratio of the exploratory drilling appears to have been 35 percent and that of the development drilling over 80 percent. Moreover, Pemex has stated that as of now it has not entirely accepted that the structures with unsuccessful wells are definitely non-productive. Other step-out wells are to be drilled at the appropriate time. So the success ratio may turn out to be even higher. 11) Several factors further enhance the petroleum prospects of the Reforma-Campeche Province: - Marine oil seeps have been found around the edges of the Campeche Bank. - The Sigsbee Knolls, where cores saturated with oil retrieved from about 3,500 m of water, are located near the northwestern edge of the Yucatan escarpment. - Giant reef trends (Fig. 3) have been mapped by seismic sparker or explosive sources methods and confirmed by drilling at the Reforma-Campeche area. They run through the Reforma-Campeche productive trend, and continue beyond the Ixchel location encircling the Yucatan Peninsula. - The giant Poza Rica field to the southwest of the Golden Lane, the production of which peaked in the 1960's, was formed in geologic conditions similar to those in the Cretaceous section of Chiapas and Tabasco. 12) Some of the fields appear to be undersaturated with gas (for example, Cunduacan, Bermudez, Sunuapa, Artesa, Sabancuy, Sitio Grande, Cactus). Their gas/oil ratios range from 1,032 to 1,837 cu. ft. of gas per barrel of oil.